System and method for thermally bonding grommets to fabric

ABSTRACT

Apparatus and methods are disclosed for bonding first and second grommet portions positioned on opposite sides of a sheet by means of localized heat and pressure applied to the first and second grommet portions. Heat and pressure may be applied by first and second pedestals positioned facing the first and second grommet portions. A registration post may secure to the first pedestal and extend through apertures in the grommet portions and sheet. The second pedestal may define an aperture for receiving the registration post. The registration post may be resiliently mounted to the first pedestal and be depressible into the first pedestal. The first and second grommet portions may have a lower melting temperature than the sheet and may bond to one another through an aperture defined by the sheet.

FIELD OF THE INVENTION

This application relates to thermally bonding flexible materials, and, in particular, to thermally bonding structures to fabric.

BACKGROUND OF THE INVENTION

Modern fabrics have many applications in many different areas. In particular, fabrics may be used to manufacture tents and other removable structures such as pavilions, awnings, and the like. Fabric is also used to make sports and outdoor equipment such as rugged outerwear, backpacks, tarps, sleeping bags, hydration bladders, and the like. Of course, fabrics are also used for most types of clothing. In many of such items, a rod, cord, or fastener must pass through a panel of fabric in order to secure the panel to another panel or some other structure. Conventionally, a grommet may surround an aperture in the panel and provide a greater degree of wear resistance as well as distribute loads around the aperture. A typical grommet includes a rigid ring that clamps edges of the aperture in order to prevent removal of the grommet. However, the bond between the grommet and panel is limited by the clamping force exerted by the grommet and can be broken due to excess tension applied to the grommet and fraying of the fabric clamped by the grommet. The rigidity of the metal grommet can also be undesirable in some applications.

An alternative approach is to bond the grommet to the panel by means of thermal bonding or adhesive. The systems and methods disclosed herein provide an improved approach for bonding grommets to a fabric panel.

SUMMARY OF THE INVENTION

In one aspect of the invention, a method for securing a grommet to a sheet includes positioning a grommet portion adjacent a surface of the sheet, the grommet portion defining an aperture. Localized heat and pressure is applied to the grommet portion effective to fuse the grommet portion to the sheet. In some embodiments, a second grommet portion is positioned adjacent a second surface of the sheet opposite the first grommet portion, the second grommet portion defining a second aperture. The sheet may define a third aperture that is larger than the first and second apertures such that first and second apertures overlap the third aperture and portions of the first and second grommet portions extend partially across the third aperture.

In another aspect of the invention, the grommet portion is placed on a first pedestal and localized heat and pressure is applied to the grommet portion by pressing a second pedestal against the sheet and grommet portion opposite the first pedestal. One or both of the pedestals may be heated.

In another aspect of the invention, a registering post extends from the first pedestal and the grommet portion is placed having the registering post within the first aperture. Likewise, the sheet may be placed having the registering post passing through an aperture defined by the sheet. The registration post may be resiliently mounted to the first pedestal such that the registration post may be depressed into the first pedestal.

A corresponding manufacturing apparatus and article of manufacture are also disclosed and claimed herein.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred and alternative examples of the present invention are described in detail below with reference to the following drawings:

FIG. 1A is an isometric view of an upper assembly for a thermal bonding apparatus in accordance with an embodiment of the present invention;

FIG. 1B is an isometric view of a lower assembly for a thermal bonding apparatus in accordance with an embodiment of the present invention;

FIG. 2 is a side cross-sectional view of a portion of an upper assembly in accordance with an embodiment of the present invention;

FIG. 3 is a side cross-sectional view of a portion of the upper assembly in accordance with an embodiment of the present invention;

FIGS. 4A through 4C are side cross-sectional views illustrating a thermal bonding process in accordance with an embodiment of the present invention; and

FIG. 5A is a top plan view of a work piece for use in accordance with an embodiment of the present invention; and

FIG. 5B is a top plan view of a work piece after a thermal bonding process in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIGS. 1A and 1B illustrate an apparatus for affixing grommets to fabric using thermal bonding. Referring specifically to FIG. 1A, an upper assembly 10 a may include an upper plate 12 and a plurality of pedestals 14 affixed to the upper plate 12. The pedestals 14 may be arranged according to a hole pattern in a work piece, such as a panel of fabric. In the illustrated embodiment, the pedestals are cylindrical; however, other cross-sectional shapes including square, hexagonal, or the like may also be used. The upper plate 12 may be embodied as a fixture plate providing a plurality of attachment points for the pedestals 14, such as a plurality of pre-drilled holes, slots, or other structures to which the pedestals 14 may secure by means of bolts, screws, quick-release fastener, or other fastening means. The pedestals 14 may secure to the upper plate 12 by non-removable fastening means such as welds or monolithic formation with the plate 12. A distal face of the pedestals 14 may define a registration aperture 16. The distal face of the pedestal 14 may be parallel to the plate 12 and the registration aperture 16 may extend perpendicular to the distal face.

Referring specifically to FIG. 1B, a lower assembly 10 b may include a lower plate 18 and a plurality of pedestals 20 also arranged according to a hole pattern of the work piece, e.g. arranged in a mirror image of the arrangement of the pedestals 14. The plate 18 and pedestals 20 may have some or all of the attributes ascribed above to the upper plate 12 and pedestals 14. Although the labels “upper” and “lower” are used to distinguish the assemblies 10 a, 10 b, the actual arrangement of the assemblies 10 a, 10 b may be reversed or the plates 12, 18 may be oriented vertically such that neither assembly 10 a, 10 b is above the other.

The pedestals 20 may include registration posts 22 extending distally from distal surface thereof, e.g. perpendicular to the distal surface. The registration posts 22 may be sized to insert without resistance into the registration apertures 16 in order to facilitate alignment of the pedestals 14 relative to the pedestals 20. In some embodiments, a pad 24 may encircle the registration post and be substantially coextensive with a distal surface of the pedestal 20, e.g. have a shape that is larger than or identical to the cross-sectional shape of the pedestal 20. Alternatively or additionally, the pad 24 may have a shape this is larger than or identical to a shape of grommets bonded according to methods described herein, which may be smaller than the cross-sectional shape of the pedestal 20. The pad 24 may be formed of a resilient, heat-resistant polymer, such as silicone.

Referring to FIG. 2, the pedestal 14 may extend outwardly from the plate 12 a distance 26. The distance 26 may advantageously reduce the amount of heat radiating from the plate 12 incident on a work piece being processed according to the methods disclosed herein. In some embodiments, the pedestal 14 may extend through, or be exposed through, an insulative layer extending over the plate 12. For example, the distance 26, or the distance 26 with insulation, may effectively ensure that a surface of the work piece experiences an increase in temperature of less than 80° C. , preferably less than 50° C., and more preferably less than 20° C. during a thermally bonding process for a grommet described herein.

The registration aperture 16 may include a tapered portion 28 that narrows with distance from the distal end of the pedestal 14. The tapered portion 28 may be embodied as a beveled or rounded area around the top of the aperture 16. The tapered portion 28 may facilitate insertion of the registration posts therein notwithstanding any slight misalignment. In this manner, provided the pedestals 14 and pedestals 20 are arranged accurately, misalignment of the plate 12 relative to the plate 18 may be accommodated by allowing relative movement of the plates 12, 18 upon insertion of the registration post 22 into the registration aperture 16.

In order to perform thermal bonding of a grommet, the pedestal 14 may be heated. Accordingly, the pedestal 14 may be formed of a material with one or both of a high heat capacity and high thermal conductivity such as steel, aluminum, or some other metal. A heating element 30 a may be embedded in the pedestal 14. The heating element 30 a may be close to the distal surface of the pedestal 14. The heating element 30 a may be arranged encircling the registration aperture 16. In some embodiments, the heating element 30 a may be external to the pedestal 14, such as mounted on a distal surface of the pedestal 14.

In some embodiments, a heating element 30 b may additionally or alternatively be embedded in the upper plate 12. In some embodiments, a heating element 30 b is embedded in the upper plate 12 adjacent each pedestal 14 and may extend over an area less than, equal to, or slightly greater than an area of a proximal end of the pedestal 14. In other embodiments, a heating element 30 b may be embodied as one or more heating elements extending across an area of the plate 12 spanning the locations of multiple pedestals 14, or all pedestals 14. In some embodiments, a heating element 30 c may additionally or alternatively be positioned above the plate 12, such as in thermal contact with the plate 12 or at a distance such that radiated heat from the heating element 30 c reaches the plate 12. A heating element 30 c may extend over an area equal to or smaller than the cross-sectional area of the pedestal 14 or may span the locations of multiple pedestals 14, or all pedestals 14. Each of the heating elements 30 a-30 c may include multiple individually powered heating elements. In some embodiments, any of the heating elements 30 a-30 c may be resistive heating element, combustion heating element (e.g. gas burner), radiant heating element, wave energy heating element (e.g. high frequency radio waves such as a high frequency (HF) welder or radio frequency (RF) welder).

Referring to FIG. 3, the pedestal 20 may likewise extend a distance 32 outwardly from the plate 18 in order to limit the area of a work piece exposed to heat during a thermal bonding process. In some embodiments, the pedestals 20 and plate 18 are not heated other than heat radiated and conducted to the pedestals 20 and plate 18 from the plate 12 and pedestals 14. In such embodiments, the pedestals 20 may be made of a material that is rigid and dimensionally stable, but may not necessarily include a thermally conductive material. However, pedestals 20 made of steel, aluminum, and other metals are suitable materials for both heated and unheated pedestals 20. Where the pedestal 20 and/or plate 18 are not heated, the height 32 may be smaller than the distance 26. In some embodiments, the pedestals 20 are omitted and the registration posts are mounted directly to the plate 18. In other embodiments, the plate 18 and/or pedestals 20 are heated according to some or all of the configurations discussed above with respect to the plate 12 and pedestals 14. In such embodiments, the plate 12 and pedestals 14 may or may not also be heated using any of the configurations described above.

In some embodiments, the registration post 22 may be slidable relative to the pedestal 20. The registration post 22 may include the same material as the pedestal 20 or a different material. For example, the registration post 22 may be made of a plastic having a melting temperature larger than a melting temperature of grommets bonded according to methods describe herein, and preferably higher than an operational temperature of the pedestal 14 when the registration post 22 is positioned within the registration aperture 16.

The pedestal 20 may define an aperture 34 extending perpendicular to the plate 18, such as coaxial with the pedestal 20. The registration post 22 may be slidably positioned within the aperture 34. A biasing member 36 may be interposed between the registration post 22 and either of the pedestal 20 or the plate 18 such that the biasing member 36 urges the registration post 22 outwardly from the aperture 34. In one example, the registration post 22 defines an aperture receiving a screw 40, or some other fastener that is threaded or otherwise secured to the plate 18. The screw 40 resists the biasing force of the spring 36 to maintain the registration post 22 within the aperture 34 while still allowing the registration post to be depressed at least partially into the aperture 34 during use.

The registration post 22 may include a tapered portion 42 that narrows with distance from the distal end of the pedestal 20. The tapered portion 42 may be embodied as a beveled or rounded area around the top of the registration post 22. The tapered portion 42 may facilitate insertion of the registration post 22 into the registration aperture 16 notwithstanding any slight misalignment.

Referring to FIG. 4A, in use a first grommet portion 44 a is placed over the pedestal 20, such as on top of the pad 24, having the registration post 22 extending through an aperture 46 a defined by the first grommet portion 44 a. The work piece 48 may likewise be placed over the first grommet portion 44 a having the registration post 22 extending through an aperture 50 defined by the work piece 48. As shown in FIGS. 1A and 1B, a plurality of pedestals 14, 20 may be arranged on the plates 12, 18. Accordingly, the work piece 48 may define a pattern of holes 50 corresponding to the arrangement of pedestals 14, 20 and the illustrated configuration of FIG. 4A will be repeated for each of the holes 50 and corresponding pedestals 20. A second grommet portion 46 b may be placed over the work piece 48 such that the registration post 22 extends through an aperture 46 b in the second grommet portion 46 b. The registration post 22 advantageously facilitated alignment of the apertures 48 a, 48 b of the grommet portions 46 a, 46 b and the aperture 50 of the work piece 48.

The process of placing of the grommet portions 46 a, 46 b and the work piece 48 in the illustrated configuration takes a significant amount of time, particularly where there are multiple apertures 50 and corresponding pedestals 20. Accordingly, some fabrication facilitates may include multiple lower plates 18 with identical arrangements of pedestals 20 may be used in combination with a smaller number of upper plates 12 having corresponding pedestals 14, e.g. one. Accordingly, while one or more of the lower plates 18 and pedestals 20 are being loaded with grommet portions 44 a, 44 b and a work piece 48, another lower plate 18 and pedestals 20 that has been previously loaded may be thermally bonded. In one contemplated configuration, a plurality of lower plates 18 are mounted to a carousel and one or both of the lower plates 18 and upper plate 12 is rotatable around the carousel. In such embodiments, the registration apertures 16 and registration posts are particularly useful for performing alignment inasmuch as the plates are free to rotate relative to one another. One or both of the lower plates 18 and upper plate 12 is slidably mounted to the carousel such that it may be brought into and out of engagement with an opposing plate.

Referring to FIG. 4B, the upper plate 12 and pedestal 14 may be brought into proximity to the pedestal 20 and plate 18. One or both of the upper plate 12 and lower plate 18 may be mounted to a slidable mount to facilitate this movement. As the upper plate 12 moves toward the plate 18, the registration posts 22 may insert within the registration apertures 16 thereby urging the pedestals 14 into alignment with the pedestals 20. The distal surface of the pedestal 14 presses downwardly on the upper grommet portion 44 b. As the pedestal 14 is brought into contact with the grommet portion 44 b, the registration post may be allowed to depress into the aperture 34, thereby depressing the biasing member 36.

One or both of the pedestals 14, 20 may be selectively heated after the pedestals 14, 20 are brought to the position of FIG. 4B. Alternatively, the pedestal 14 may be maintained at an operational temperature such that as the pedestal 14 and pedestal 20 are brought to the configuration of FIG. 4B the thermal bonding process begins. In embodiments where only the pedestal 14 is heated, the pad 24 may act as a heat conductor to distribute heat transmitted through the grommet portions 44 a, 44 b and work piece 48 over the grommet portion 44 a. In some embodiments, the pad 24 may operate as a thermal insulator. The pad 24 may be an insulator with a heat reflective layer on its outer surface to concentrate the heat on the grommet portions 44 a, 44 b. The pad 24 may be resilient and flexible and thereby accommodate slight non-parallel arrangement of the distal faces of the pedestals 14, 20 by avoiding excess pinching of the work piece 48 and grommet portions 44 a, 44 b due to the non-parallel arrangement. Where the pedestal 20 is made of steel, aluminum, or other material with high thermal conductivity and the pedestal 20 is unheated, the pedestal 20 may act as a heat sink and delay the thermal bonding process. Accordingly, a pad 24 embodied as a thermal insulator to reduce the amount of heat lost to the pedestal 20. In some embodiments, the pedestal 20 may be made of a rigid but low thermally conductive material and the pad 24 is omitted.

As shown in FIG. 4C, the apertures 46 a, 46 b may be smaller than the aperture 50 in the work piece 48 such that the grommet portions 44 a, 44 b are bound to one another inside the aperture 50. The grommet portions 44 a, 44 b may additionally or alternatively bond to the work piece 48. For example, the work piece 48 may include a woven material such that the grommet portions 44 a, 44 b flow around the fibers of the material upon melting. The work piece 48 may also include a thermoplastic such that mixing of the grommet portions 44 a, 44 b with the material of the work piece 48 creates a bond therebetween. In some embodiments, the grommet portions 44 a, 44 b have a lower melting temperature than the work piece 48 such that work piece 48 does not melt during the bonding process or melts to a lesser extent than the grommet portions 44 a, 44 b. For example, the time in which heat is applied to the grommet portions 44 a, 44 b and the work piece 48 may have a duration such that the work piece 48 does not melt or melts to a lesser extent than the grommet portions 44 a, 44 b. In some embodiments, the grommet portions 44 a, 44 b are formed of thermoplastic polyurethane, however other thermoplastics pay also be used. In some embodiments, the bonded grommet portions 44 a, 44 b and work piece 48 remain flexible after the bonding process. In other embodiments, the grommet portions 44 a, 44 b are formed of a material and have a thickness such that the bonded grommet portions 44 a, 44 b and work piece 48 are substantially more rigid than the work piece 48 alone.

Referring to FIGS. 5A and 5B, as noted above, the work piece 48 may include a plurality of holes 50 and the pedestals 14, 20 may be arranged on the plates 12, 18 to align with the plurality of holes 50. After thermal bonding, as shown in FIG. 5B, each aperture 50 is surrounded by a grommet formed by the grommet portion 44 a on one surface and the grommet portion 44B on an opposing surface having the apertures 46 a, 46 b of the grommet portions 44 a, 44 b completely overlapping the apertures 50.

The systems and methods described herein advantageously do not affect a major portion of the work piece. Stated differently, the temperature of one or both of the pedestals 14, 20 during the thermal bonding process and the duration of the thermal bonding process may result in an affected area 52 of the work piece 48 that is heated a significant amount during the bonding process, e.g. experiences a temperature increase of more than 80° C. in some embodiments, of more than 50° C. in other embodiments, and more than 20° C. in still others. In some embodiments, the affected area 44 a extends no further than an edge of the grommet portions 44 a, 44 b. In other embodiments, the affected area 44 a extends outwardly from an edge of the grommet portions 44 a, 44 b a distance less than 25%, preferably less than 10%, and more preferably less than 5% of the widest diameter of either of the grommet portions 44 a, 44 b. By limiting the size of the affected area 52, shrinkage of the work piece 48 is reduced and the dimensions of the final reinforced work piece 48 can therefore be more reliably controlled. The size of the affected area may be controlled by a selection of one or more of a diameter of the distal surfaces of the pedestals 14, 20, a maximum temperature of the bonding process, and a duration of the bonding process (i.e. how long heat and pressure is applied to the grommet portions 44 a, 44 b and work piece 48). Accordingly, a bonding process may include selecting some or all of pedestal diameters, maximum temperature, and bonding duration effective to achieve an affected area 52 as described above.

While the preferred embodiment of the invention has been illustrated and described, as noted above, many changes can be made without departing from the spirit and scope of the invention. For example, items other than grommets may be bonded to a sheet using the methods disclosed for purposes of reinforcement or other uses. Accordingly, the scope of the invention is not limited by the disclosure of the preferred embodiment. Instead, the invention should be determined entirely by reference to the claims that follow. 

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:
 1. A method for securing a grommet to a sheet, the method comprising: positioning a grommet portion adjacent a surface of the sheet, the grommet portion defining an aperture; and applying localized heat and pressure to the grommet portion effective to fuse the grommet portion to the sheet.
 2. The method of claim 1, wherein the grommet portion is a first grommet portion and the aperture is a first aperture, the method further comprising positioning a second grommet portion adjacent the sheet opposite the first grommet portion, the second grommet portion defining a second aperture; wherein applying localized heat and pressure to the first grommet portion effective to fuse the first grommet portion to the sheet further comprises applying localized heat and pressure effective to fuse the first and second grommet portions to the sheet.
 3. The method of claim 2, wherein: the sheet defines a third aperture that is larger than the first and second apertures, the method further comprising positioning the third aperture such that first and second apertures overlap the third aperture and portions of the first and second grommet portions extend partially across the third aperture; and applying localized heat and pressure effective to fuse the first and second grommet portions to the sheet further comprises applying localized heat and pressure effective to fuse the first and second grommet portions to one another through the third aperture.
 4. The method of claim 1, wherein positioning the grommet portion adjacent the surface of the sheet comprises: placing the grommet portion over a first pedestal; and placing the sheet over the first pedestal.
 5. The method of claim 4, wherein applying localized heat and pressure to the grommet portion further comprises: pressing a second pedestal against the sheet and grommet portion opposite the first pedestal; and heating one or both of the first and second pedestals.
 6. The method of claim 4, wherein: a registering post extends from the first pedestal; placing the grommet portion over the first pedestal further comprises placing the registering post within the aperture; and placing the sheet over the first pedestal further comprises placing the registering post in a second aperture defined by the sheet.
 7. The method of claim 6, wherein applying localized heat and pressure to the grommet portion further comprises: pressing a second pedestal against the grommet portion and sheet opposite the first pedestal effective to depress the registering post into the first pedestal; and heating at least one of the first and second pedestals;
 8. The method of claim 7, wherein the second pedestal defines a registration receiver for receiving a portion of the registering post.
 9. The method of claim 8, wherein at least a portion of at least one of the registering post and registration receiver is tapered.
 10. The method of claim 4, wherein placing the placing the grommet portion on the first pedestal further comprises placing the grommet portion adjacent a heat conducting member positioned on the first pedestal.
 11. The method of claim 10, wherein the heat conducting member comprises a silicone ring.
 12. The method of claim 1, wherein the grommet portion has a lower melting point than the sheet.
 13. An apparatus for securing grommets to a sheet, the apparatus comprising: a plurality of first pedestals affixed to a first fixture and arranged according to a hole pattern defined by the sheet; a second fixture positionable opposite the first fixture to apply pressure to the first pedestals; and at least one heating element in thermal contact with at least one of the plurality of first pedestals and the second fixture.
 14. The apparatus of 13, wherein the plurality of first pedestals have a distal surface shaped substantially identically to the grommets.
 15. The apparatus of claim 13, wherein the first pedestals include registration posts extending from a distal surface thereof.
 16. The apparatus of claim 15, wherein the first pedestals define first apertures for receiving the registration posts, the apparatus further comprising a plurality of biasing members interposed between the first pedestals and the registration posts.
 17. The apparatus of claim 15, wherein: at least distal portions of the registration posts are tapered; a plurality of second pedestals are affixed to the second fixture and arranged according to the hole pattern defined by the sheet; and the second pedestals define apertures for receiving at least portions of the registration posts.
 18. The apparatus of claim 13, further comprising a plurality of second pedestals affixed to the second fixture and arranged according to the hole pattern defined by the sheet.
 19. An article of manufacture comprising: a first grommet portion defining an aperture; a second grommet portion defining a second aperture; a sheet defining a third aperture; wherein the sheet is positioned between the first and second grommet portions, the first and second grommet portions being bonded to the sheet and bonded to one another through the third aperture; and wherein the first and second grommet portions are bonded to the sheet by local application of heat and pressure exclusively to an affected area substantially limited to an area of the sheet coextensive with the first and second grommet portions.
 20. The article of manufacture of claim 19, wherein the first and second grommet portions include a first material and the sheet includes a second material, the first material having a lower melting point than the second material. 